A writer, philanthropist, and activist, Joan Parker
was also a muse extraordinaire to her late husband, mystery writer Robert B. Parker, and the inspiration for Susan Silverman, the fictional girlfriend of Spenser, the private investigator who was her husband’s greatest creation.

Mrs. Parker, who died of lung cancer Wednesday in Massachusetts General Hospital, was 80 and lived in a large Cambridge house she had shared with her husband in an unusual, and unusually public, arrangement after a two-year separation three decades ago.

Until his death, in 2010, they lived in separate private areas, went on dates with each other every week, and pursued individual endeavors, all the better to keep his celebrity as one of the world’s best-known writers from consuming them both. They did not hide the arrangement in interviews, and throughout a romantic relationship that began when they attended Colby College, in Maine, the Parkers bantered as deftly as their fictional counterparts and were often as buoyantly profane.

“They were a bit of an act, as some people are together,” said Helen Brann, Mr. Parker’s agent for many years and the couple’s longtime friend. “They fed each other lines without meaning to and were great, great fun. Some couples, after 15 minutes you think, ‘Oh dear, we’ve had enough of Fred and Ginger.’ With them, it was unforced.”

Long an active philanthropist in the arts and with organizations involved with Boston’s gay and lesbian community, Mrs. Parker for two decades cochaired Community Servings, a nonprofit providing emergency food and nutrition for the acutely ill, their dependents, and caregivers. The organization, which honored her last year with a LifeSavor Award, began in 1989 by focusing on those with HIV and AIDS.

“She was very deeply a mother, very deeply a family person,” said the Parkers’ son David of New York City, a choreographer who directs his own dance company, The Bang Group. “She was so outgoing and so social and so public, and she did so much great philanthropic work that it’s easy to see her in that context, and many people love her that way.”

All her philanthropy, however, was tied to her love of David and the Parkers’ other son, Daniel of Ashland, Ore., an actor who is a member of the Oregon Shakespeare Festival.

Mrs. Parker “supported dance in Boston because I’m a choreographer,” David said. “She supported theater in Boston because Dan is an actor. She supported Community Servings and PFLAG because Dan and I are gay. Everything had to make sense to her on that level. . . . She wanted the world to work for us in every way we cared about.”

In 1996, Dan Parker told the Globe that “every gay man struggling to come out of the closet should dream of having her as his mother.”

“For me, she was a complete role model of how to live your life: large, and with commitment and fearlessness,” he said Thursday.

Coauthor with her husband of many scripts for television adaptations of his novels, Mrs. Parker also co-wrote with him “Three Weeks In Spring.” The 1978 nonfiction book recounted her first bout with cancer and first mastectomy and was as unsparing as any of Mr. Parker’s Spenser novels. Written novelistically and narrated in the third person, the book detailed the ways Mrs. Parker faced the diagnosis and surgery.

“She knew with even more certainty that he would feel exactly the same about her,” the narration recounts. “She never doubted that he would desire her with the intensity that he always had. She knew it would never matter to him. But to everyone else, she knew it would.”

Desire was an integral part of the couple’s marriage. Unlike some in their generation who shied from referring to their intimate hours, the Parkers were frank. Did millions of readers think that Susan Silverman’s sex life was based on Mrs. Parker’s? “I’ve toned it down for publication,” Robert Parker told columnist George F. Will in 1987.

In 1996, when they were 63,
Robert Parker explained their separate-floors arrangement by telling the Globe: “I never want to sleep with my wife again, but I hope to continue making love to her forever.”

At times the Parkers could be challenging to quote in family publications. For them, polite company was never so polite that it could not be enlivened with language that would make a minister blush.

“Her foul mouth and her swearing were so funny, delicious, and such a part of her,” Dan Parker said. “She was a genius philanthropist, but also could have a mouth of a sailor, and the dichotomy of that was just brilliant. She swore like no other, and it was with great aplomb. She was just a fearless woman, a gorgeous woman with a great heart.”

Born in Pittsfield, Joan Hall was the younger of two sisters. She and Robert Parker met at a birthday party when they were 3 and reconnected more memorably at Colby, during a dance.

“I thought he was thoroughly revolting,” she told the Globe in 1979. “He was a greaser who never stopped chewing gum.” Still, she told a friend she was sure “he was more than the Lucky Strikes-rolled-up-in-the-sleeve type. We began dating when we were seniors.”

They married in 1956. “I was seduced by Ace’s mind,” she told the Globe in 1981, using her husband’s nickname. “He was very smart and he knew it, and I reveled in that. He was the only man who didn’t bore me.”

She studied psychology at Colby and graduated from Tufts University with a master’s in early childhood growth. Mrs. Parker was working for the state Department of Education when she quit to write television scripts based on her husband’s books. They founded Pearl Productions and co-wrote the 1990 book “A Year at the Races.”

It was she who encouraged him to get a doctorate so he could teach at the college level, and she who offered a characteristically profane benediction when he finished the manuscript of his first Spenser novel: “ ‘Holy [expletive],’ I said to him, ‘this is like a real book,’ ” she recalled in 1981.

A memorial service will be announced for Mrs. Parker, who in addition to her sons leaves a grandson, Spenser, named for the fictional investigator his grandfather created.

For many fans, Mrs. Parker and her husband were inseparable from Silverman and Spenser. At times, the assumption could get irritating.

“There are four of us now,” she told the Globe in 1981, “me and Ace and Spenser and Susan. She is a person in my life. I am trying to separate from her. Spenser and Susan are a composite of both he and I. But in terms of real life, we are very far away from Susan and Spenser. I like her OK, but what I dislike is the assumption that Susan and I are the same person. Sure, there are some similarities. The repartee, back and forth, between Susan and Spenser is like the way Ace and I have of talking publicly to each other. But I am me. I am not Susan Silverman.”

Two years earlier, Mrs. Parker told the Globe that Silverman could be improved: “I’ve actually grown to like her. But she still ain’t bitchy enough.”